A conventional nozzle for gas shielded arc welding is integrally formed of a metal, chiefly of copper, and is connected to the forward end portion of a welding torch when used. When spatters are produced by welding, they tend to adhere to the metal nozzle, and sometimes a part of the metal nozzle with high-temperature spatters adhered thereto melts and the nozzle may be easily broken. Such a damaged nozzle easily introduces further spatters. In addition, when spatters adhere to the inner surface of the nozzle, the passage of the shielded gas is narrowed, and the contact tip and the inner surface of the nozzle are apt to be bridged due to the spatters which have adhered thereto. If the contact tip and the inner surface of the nozzle are bridged, the contact tip and an object which is being welded will be short-circuited through the nozzle, inconveniently resulting in damage to the main body of the torch, not to mention the nozzle itself.
This brings about such disadvantage as the financial loss caused by damage of the apparatus and the mental pressure felt by an operator due to the need for him to constantly take into consideration the possibility of short-circuiting during a welding operation.
Furthermore, it is necessary to suspend the welding operation in order to remove the spatters which have adhered to the nozzle, this work requiring much labor since the spatters adhere fast to the nozzle.
The above-described problems are remarkably seen especially in CO.sub.2 arc welding which has a strong tendency to produce spatters. In the case of utilizing CO.sub.2 arc welding in the automatic welding by a robot or the like which has recently been used increasingly widely, one of the important technical problems to be solved is that the adhesion of spatters to a nozzle and damage of the apparatus caused thereby should be prevented from the viewpoint of facilitating continuous operation extending over long periods.
Japanese Utility Model Unexamined Publication No. 111473/1982 (JP-U-57/111473) discloses means for preventing spatters from adhering to the inner peripheral surface of a nozzle. That is, the inner surface of a metal nozzle is coated with a heat-resistant and nonconductive material. This device makes it difficult for spatters to adhere to the inner peripheral surface of a nozzle. However, since there is a large difference between the thermal expansion coefficient of a heat-resistant non-conductive material and that of a metal, the heat-resistant non-conductive material coated on a nozzle which is subjected to repeated thermal shock often breaks or is peeled off, thereby restricting the life of the nozzle.
It might be suggested that the entire nozzle should be formed of a heat-resistant non-conductive material such as ceramics. Ceramics are, however, easily broken when they become nicked or the like, as is known. Therefore, it is considered that a nozzle having a configuration like a conventional one formed of ceramics would have limited durability when adapted to practical use.
The present applicant proposed a nozzle which uses a ceramic nozzle member in Japanese Patent Laid-Open No. 60-200573 published on May 23, 1985. This nozzle is composed of a support ring and a ceramic nozzle member. The support ring is screwed into the forward end portion of a welding torch, and a holding claw portion having an engaging projecting portion is provided at the forward end portion of the support ring. A concave groove is provided on the outer peripheral portion of one end of the ceramic nozzle member, and the engaging projecting portion is inserted into the concave groove, whereby the nozzle member is fixed to the welding torch.
This nozzle can eliminate the above-described problems, but since it utilizes concavo-convex engagement, it is required that the nozzle member posseses high dimensional accuracy. Therefore, it disadvantageously takes a long time to produce a nozzle member, resulting in a costly nozzle member.